In the hot forming of sheet steel blanks to produce a shaped body, for example, a cross beam for a shock absorber system or some other part of a motor vehicle, the method can involve the techniques described for example in German Patent DE 24 52 486 C2. In this system, a press forming of the sheet steel blank in a die and in-the-die hardening of the shaped steel body is described for workpieces of boron-alloyed steel. The steel blank is heated to a temperature above the AC3 temperature, namely the temperature at which in the alloy steel the conversion of ferrite to austenite is complete, and then is held in the die for cooling over a period of less than five seconds for hardening. The rapid cooling in the layer shaping die, by indirect cooling, e.g. water cooling of the upper and lower die members of the forming press, results in a martensidic or bainitic fine grain structure. The result can be a product of small thickness of the material from which the shaped steel body is formed, high dimensional stability and high strength.
While the aforedescribed method has been found to be successful in practice, there are many parts of a vehicle where energy-absorbing members are used in the chassis and in parts of the vehicle connected to the chassis that require not only the high strength and good yielding characteristics or ductility, that this method can afford but also the high shape stability and the capacity to use the technique for mass production.
However, in the past these hot formed and tool-hardened components frequently had to be joined to other members. In the case of metal members, this generally required a weld or screw connection. Both of these joining techniques required separate steps in the manufacturing process to effect the joining. In addition, the heat applied by welding could result in dimensional variations, loss of hardness and other drawbacks. In fact, both attachment techniques frequently resulted in a weakening of the zone at which the attachment occurs. A drawback of the screw connection is that the screws themselves create locations at which there can be water penetration, rust formation and loss of strength. Both the welding technique and the screw connection technique had negative affects of the reliability and durability of the assembly.